The present invention relates to an electroluminescent device having a luminescent layer comprising a luminescence substance, capable of directly converting an electric energy into a light energy by application of an electric field and capable of providing a surface luminescence of a large area different from conventional incandescent lamps, fluorescent lamps or light emitting diodes.
The electroluminescent device can be classified, depending on the difference of the luminescence excitation mechanism into the following two groups: (1) an AC driving electroluminescent device of exciting a luminescent material by the local transfer of electrons or holes in a luminescent layer and emitting light only under an AC electric field, and (2) a DC deriving electroluminescent device of exciting a luminescent material by the injection of electrons and holes from electrodes and recombination of the electrons and holes in a luminescent layer, and operating under a DC electric field. The AC deriving electroluminescent device generally uses, as a luminescent material an inorganic compound comprising ZnS to which Mn or Cu is added, but it involves various problems such that it requires an AC electric field at a voltage of higher than 200 V for driving and expensive production cost, and it has an insufficient luminance or durability.
From since a thin film of an organic compound has been used as the luminescence layer, a DC deriving electroluminescent device showing high luminance is obtainable. For instance, Japanese Patent Application Laid-Open (KOKAI) 59 195393 (1984), U.S. Pat. No. 4,539,507, Japanese Patent Application Laid-Open (KOKAI) 63-295695 (1988), U.S. Pat. No. 4,720,432 and Japanese Patent Application Laid-Open (KOKAI) 63-264692 (1988) disclose electroluminescent devices comprising anode, organic hole transporting region, organic electron luminescent region and cathode. As typical examples of the materials used for the device, there can be exemplified an aromatic tertiary amine as the organic hole transporting material and aluminum trisoxine as the organic electron luminescent material.
Further, an electroluminescent device comprising an anode, an organic hole transporting layer, a luminescent layer, an organic electron transporting layer and a cathode is reported in JPn. Journal of Applied Physics. Vol. 27, P 713.about.715. As the material used for the device, there can be exemplified, for example, N,N'-diphenyl-N,N'-bis(3 methylphenyl)-1,1'-biphenyl-4,4'-diamine as the organic hole transporting material, 3,4,9,10-perylene tetracarboxylic acid bisbenzimidazole as the organic electron transporting material and phthaloperynone as the luminescent material.
These embodiments point out a necessity for studying various characteristics of such organic compounds and effectively combining the characteristics to provide an electroluminescent device in order to use organic compounds for the hole transporting material, luminescent material and electron transporting material. In other word, they show a necessity for the research and development of organic compounds over a wide range.
Further, the history for the studies of the DC deriving electroluminescent device using the organic compounds including the above-mentioned embodiments as the luminescent material is short and, accordingly, it can not be said that a sufficient studies have been made for the materials and for the formation of electroluminescent devices. At present, there are a lot of technical problems to be dissolved such as a further improvement of the luminance, diversification of emission wavelength in order to precisely select the luminescent hues of blue, green and red in view of an application to a full color display, and an improvement in the durability.
In view of the situations in the prior arts, it is an object of the present invention to provide an electroluminescent device having diversification in the emission wavelength, and exhibiting various luminescence hues and excellent in the durability.
As a result of the present inventors' earnest study on the constituent elements for the luminescent layer for resolving the foregoing technical problems, it has been found that the foregoing object can be attained by an electroluminescent device comprising an anode, a cathode and one or plurality of organic compound layer sandwiched therebetween, wherein at least one of the organic compound layers comprises a constituent element of an organic compound represented by the following general formula (I): ##STR2## (wherein A.sup.1 and A.sup.2 each represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group which may be identical or different with each other, Ar represents a substituted or unsubstituted pyrenyl group and n represents 1 or 2). Based on this finding, the present invention has been attained.